Prepare the broth, if necessary.,______,Add the pancetta.,Cook, stirring frequently, over medium heat until golden, about 10 minutes.,Add the onion and celery and cook, stirring occasionally, until softened, about 5 minutes.,Add the mushrooms, 2 tablespoons of the parsley, and the garlic.,Cook, stirring often, until the mushroom juices evaporate, about 10 minutes.,Stir in the potatoes, salt, and pepper.,Add the broth and bring to a simmer.,Add the barley and cook, uncovered, over low heat for 1 hour or until the barley is tender and the soup is thickened.,Sprinkle with the remaining barley and serve hot.